There is a fundamental relationship between alpha decay energy (which is shared between both the alpha and nuclear recoil) and the half-life of the decay. It's called the Geiger-Nuttall law, and can be derived (by people with better understanding of quantum mechanics than me) from a simple model of an alpha particle bouncing around inside a nuclear potential with quantum tunnelling.
The half life is exponentially dependent on decay energy. High energy decays are produced from nuclei with very short half lives. For any nuclide likely to be observed in nature, or outside an accelerator lab, the half-life vs energy relationship is more or less flat, and all alpha decays have energies in a narrow range of abut 3-7MeV.
Thanks a lot creswell for the clarification. But this document confuses me http://dbserv.pnpi.spb.ru/elbib/tablisot/toi98/www/decay/table3.pdf here the mentioned energies extend all the way upto 11 MeV and on the lower side to 1.8KeV. Please correct me if my interpretation of the table is wrong.
That table must be in keV (though it doesn't seem to say what energy units it's using), so that's 1.8 - 11.7 MeV. I don't know how many nuclei are on that table in total (about 2000?), but there are only 18 with 7MeV. So, about 75% of nuclei within the 3-7MeV range, and a lot of those outside that range quite exotic.
Alan, I couldn't understand the meaning of exotic, suppose If I have to design a detector readout system for alpha spectroscopy can I discard pulses corresponding to these exotic nuclei right away? please clarify
By 'exotic' I meant very unusual - superheavy transuranics (the table, for example, has 255No), or nuclei far from the valley of stability (215Th, for example).
These aren't nuclei you will observe in an environmental sample, nuclear waste characterisation and the like. These nuclei are formed in laboratories, using particle accelerators.
One more help Alan, where can I find a complete list of all the possible alpha emitting isotopes (i.e. those which have energies within this 3 Mev to 7 MeV range)? most of the documents I have give just list of frequently used laboratory type source.
Any searchable nuclear database will give you such a list. I use Janis http://www.oecd-nea.org/janis/ as a tool for searching nuclear data. I've attached the output of a search on all alpha decay lines from the JEFF 3.11 database.
- Badges
- Science topic
- Similar topics
- Methodology
- Laboratory